Did the Big Bang happen?

[Mister Agenda]

So, what I’m wondering is… Is it possible that there was no Big Bang and that the universe simply always existed?

We seem to have a lot of evidence of the universe expanding. We also have evidence of cosmic background radiation from when the universe was hot. But do we have evidence that these things started from a singularity? Is that part of all of it truly known fact? How can this even happen since in order for such an event to happen it would have to be “outside” time, because it would be before the expansion of the space time fabric?

The evidence for the Big Bang/Initial Expansion is very robust, but strictly speaking, what happened before the expansion isn't really part of the theory, which describes what happened when the hot dense universe began to expand. How long the hot dense version of the universe was there, 'where' it came from, whether some version of the universe has always existed...these are mysteries. The Initial Expansion theory does a pretty good job at what it's supposed to do: explain how our universe came to be the way it is.

So it's possible there was a Big Bang AND the universe simply always existed.